1. Field of the Invention
The invention relates to a fluid pressure regulating device and a fuel supply system that uses this fluid pressure regulating device. More particularly, the invention relates to a fluid pressure regulating device suited to regulating fuel pressure when supplying fuel for an internal combustion engine from a fuel pump to a fuel injection valve.
2. Description of Related Art
A fuel supply system of an internal combustion engine mounted in a vehicle or the like typically supplies fuel from a fuel pump to an injector (i.e., a fuel injection valve), and regulates the fuel pressure inside a fuel supply passage using a pressure regulator, i.e., a fluid pressure regulating device. In this kind of fuel supply system, the housing of the pressure regulator is divided by a diaphragm into a pressure regulating chamber and a back pressure chamber. Urging force in a valve opening direction is applied to the diaphragm from fuel pressure inside the pressure regulating chamber, while urging force in the valve closing direction is applied to the diaphragm from the back pressure chamber side. The fuel supply system regulates the fuel pressure inside the pressure regulating chamber to a predetermined set pressure that is based on the urging force from the back pressure chamber side, by discharging some of the fuel inside the pressure regulating chamber according to the displacement of the diaphragm.
Japanese Patent Application Publication No. 2009-108684 (JP-A-2009-108684) describes one such fluid pressure regulating device and fuel supply system. This described device includes first and second diaphragms that divide the inside of a housing into three pressure chambers, a valve body that is attached to the first diaphragm so as to open and close a pressure regulating discharge outlet inside a first pressure chamber between the housing and the first diaphragm, a pressure receiving body that is connected to the valve body via a connecting passage arranged in a second pressure chamber between the first and second diaphragms, and is fixed to the second diaphragm, and a spring that is provided in a third pressure chamber between the housing and the second diaphragm and that urges the pressure receiving body in a valve closing direction. In this device, the regulated fuel pressure can be switched in a plurality of stages by controlling the supply pressure to the second and third pressure chambers.
Also, Japanese Patent Application Publication No. 2002-310025 (JP-A-2002-310025) describes a device that feeds fluid that has been regulated to an assist pressure value by a second pressure regulator into a back pressure chamber of a first pressure regulator, so as to assist the urging force of urging means of the first pressure regulator, thereby increasing the set pressure. As a result, the set pressure value is able to be increased without replacing an urging member or pressure regulator.
Furthermore, Japanese Patent Application Publication No. 2007-218222 (JP-A-2007-218222) describes a device that has an electromagnetic valve that functions as a cut-off valve provided in a return line of a back pressure chamber that introduces fluid for back pressure. When it is determined that fuel vapor may be produced, pressure on the back pressure chamber side of the pressure regulator is increased to increase the fuel supply pressure to the injector to a level that suppresses the production of fuel vapor. As a result, idle speed is prevented from becoming unstable due to the production of fuel vapor when the engine is restarted at a high temperature.
However, with a fluid pressure regulating device provided with a plunger and a second diaphragm on the back pressure chamber side, and a fuel supply system that uses such a fluid pressure regulating device, the inside of the housing of the pressure regulator is divided into first to third pressure chambers that are adjacent to each other in the displacement direction of the diaphragm. As a result, it is difficult to make the device compact, which in turn makes the device difficult to install. Also, each of the first to third pressure chambers requires a fluid inlet and a fluid outlet, so the passage configuration becomes extremely complex.
Also, with a fluid pressure regulating device in which fluid pressure is introduced to the back pressure chamber side in the housing, and a fuel supply system that uses such a fuel pressure regulating device, fluid pressure is also necessary at places other than the pressure regulating chamber when the pressure is regulated to a high pressure. As a result, extra fuel is necessary, and a greater number of portions need to be sealed, which leads to an increase in cost.
Moreover, with a fuel supply system in which an electromagnetic valve is provided in a return line for returning excess fuel that has passed through the fuel gallery from the pressure regulator to the fuel tank, the section of the fuel passage in which the pressure is increased to a high pressure during engine startup becomes wide, and a seal that can withstand the high pressure over that entire area is necessary, which leads to an increase in the cost of the fluid pressure regulating device and the fuel supply system.